Possible Clues:

• Musical segment
• When "Vissi d'arte" is sung in 39-Down
• When Romeo and Juliet get married
• Theater's second stage?
• When "The Room Where It Happens" happens
• Pop Secret competitor
• When to hear "SOS" in "Mamma Mia!"
• Final part of most Broadway musicals
• Conclusion of ''Cats''
• When Rosencrantz and Guildenstern first appear